We had a perfect shed last month depite humidity dropping to the 30s due to a dry spell plus the heat lamp. How I raised humidity (in a glass tank) was by having 2 constantly wet paper towels in the tank, along with the water bowl. Rather than spraying a mist, I'd occasionally dab the wet paper towels at various spots on the substrate (newspaper plus paper towel), but not actually inside the warm hide where BP was.

It worked! Good luck!